The European Union has been urged to act against Lebanon's Hizbollah movement after Bulgaria blamed it for an attack on a busload of Israeli tourists last year.

Five Israelis and their Bulgarian driver were killed as they travelled from the airport to their hotel in the Black Sea resort of Burgas on July 18.

Bulgarian interior minister Tsvetan Tsvetanov said the cell which carried out the remote-control bombing included one suspect who entered the country with a Canadian passport and another with one from Australia.

"We have well-grounded reasons to suggest that the two were members of the militant wing of Hizbollah," he said.

The Shia Muslim militant group and political party, which emerged in response to Israel's 1982 invasion of Lebanon, has been linked to attacks and kidnappings on Israeli and Jewish interests around the world but has not been listed as a banned terrorist organisation by the EU.

Image Caption:A remote-control device exploded on the bus

Israel's Prime Minister Benjamin Netanyahu urged Europe to draw the "proper conclusions" about the "true character of the group" following the Bulgarian investigation.

The White House also called on Europe to take "proactive action" to disrupt the group's finances and operational network.

In a statement, Foreign Secretary William Hague said: "It is important that the EU respond robustly to an attack on European soil.

"Every act of terror is an attack on our shared values. In committing an attack, terrorists seek to undermine our resolve, but they should only serve to strengthen it.

Image Caption:CCTV was released of the suspected bomber at the airport

"The Home Secretary and I will be talking to our EU colleagues about the measures we can now take to continue to make our citizens safer."

Catherine Ashton, the European Union's high representative for foreign and security policy, said the EU needed to assess the implications of the investigation and stressed that any decision on adding Hizbollah to the EU list of terrorist organisations would require a unanimous decision by the foreign ministers of the 27 EU countries.

Hizbollah has denied involvement in the Bulgaria bombing, which killed the suspected bomber, a pale-skinned man wearing a baseball cap and dressed like a tourist.

But Europol Director Rob Wainwright said two counterfeit US driver's licences that were found near the bombing scene were traced back to Lebanon, where they were made.

He said forensic evidence, intelligence sources and patterns in past attacks all point to Hizbollah's involvement in the blast.

"The Bulgarian authorities are making quite a strong assumption that this is the work of Hizbollah.

"From what I've seen of the case - from the very strong, obvious links to Lebanon, from the modus operandi of the terrorist attack and from other intelligence that we see - I think that is a reasonable assumption."

Lebanese Prime Minister Najib Mikati condemned the attack and said his country would co-operate fully.